The surgical hat Mack wears while operating on Ward is normally supposed to keep hair (and sweat) from falling into a clean surgical feed. As Mack is bald, it is a pointless prop, especially so when his mouth and hairy beard aren't being covered by a surgical mask.
Mack tells Piper the six-digit door code, and the door opens before Piper presses all six buttons.
Elena discovers that she suffers intense pain when attempting to use her new artificial arms in conjunction with her super speed powers. This was actually her second time using these abilities together. She should have discovered the problem during the previous episode.